"T not defined" when defining parametric one-line function with return type

Internals & Design
1

I noticed the following seemingly weird error when defining an abstract generic type:

abstract type SomeAbstractType{T} end
func(x::SomeAbstractType{T})::Bool where {T} = error("func is not implemented.")

and getting an error like “ERROR: UndefVarError: T not defined”.
However, if the return type is removed then no error occurs:

abstract type SomeAbstractType{T} end
func(x::SomeAbstractType{T}) where {T} = error("func is not implemented.")
# func (generic function with 1 method)

What’s going on here? (I use Julia 1.5)

2

seems to be a parsing edge case?

julia> function func(x::SomeAbstractType{T})::Bool where {T}
           error("func is not implemented.")
       end
func (generic function with 1 method)
3

Yes, rewriting the function definition with function keyword seems to eliminate the problem. Is there a bug in the parser, or is it designed to be so?

4

It’s a known issue: https://github.com/JuliaLang/julia/issues/21847

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